An application of bar code symbology with which most consumers are familiar is the representation of a product id. Typically, when a consumer purchases a product the bar code word, a series of black and white bars that are representative of the product id, is detected by a laser system that communicates the product id to a computer system that in turn, supplies the price of the product.
A bar code symbology is set of symbols, similar to an alphabet, that can be combined to form words that represent information. Bar code symbols are composed of elements, black and white bars of varying width that absorb and reflect light, respectively. Numerous optical devices that take advantage of the varying reflectivity of the black and white bars have been developed to read bar code symbols. A typical bar code reading device is the light pen, which is comprised of a laser diode for directing a beam of light to the bar code symbol and a photodetector for generating a digital signal representative of the presence or absense of reflected light. Providing the bar code reading device moves across the bar code symbol at a relatively constant speed, the relative durations of the signals generated by the photodetector are representative of the relative widths of the black and white bars that comprise the bar code symbol. The absolute duration of the signals are dependent upon the speed with which the reading device scans the bar code symbol. The signal produced by the photodetector is input to a bar code decoder that translates the signal into a form that is acceptable to a computer. For the bar code decoder to translate the input signals into a format acceptable to a computer it must be designed according to the following three parameters that characterize the input signals: the bar code symbology being employed, the speed with which the reading device is scanning, and the polarity of the signals (e.g. whether a logical-zero signal is representative of a white bar or black bar). Based upon these three parameters the bar code decoder can be designed to translate the input signals into a form acceptable to the computer. Typically, the bar code decoder present in any given system is designed to process signals representative of symbols associated with one specific bar code symbology (there are several bar code symbologies in existence), signals whose absolute duration is defined by the particular scanning speed of the reading device employed in the system, and signals with a defined polarity.
A problem, however, arises when bar code symbols and the associated optical bar code reading devices are used in environments where there is a high concentration of particulates that tend to scatter or disperse the laser light beam used to detect the bar code symbol. Similarly, bar code symbols and optical readers cannot be used in situations where foreign objects are interposed between the reader and the bar code symbol thereby blocking the light beam.
Systems that avoid this problem include radio frequency identification (RFID) systems, which are substantially unaffected by the presence of foreign objects or particles. Representative of RFID systems are U.S. Pat. No. 4,333,072 to Beigel for an "Identification Device", U.S. Pat. No. 4,663,625 to Yewen for a "Passive Tag Identification System and Method" and the electronic label and sensor produced by Nedap. Typically, these RFID systems are comprised of a passive tag (i.e. without an independent power source) that contains the relevant information and a sensor that outputs a RF carrier signal. When the tag is brought near the sensor, inductive coupling occurs and the tag is powered by the RF carrier signal being emitted by the sensor. While the tag is active, it modulates the RF carrier with the information. A detector located in the sensor receives the modulated RF carrier signal. However, the modulated RF signals of such RFID systems are not in the digital format accepted by the standard bar code decoder.
A system is generally described in a publication entitled "Description And Operating Instructions For The Symbollink LL-310 Wand Emulator Interface Controller" of Symbol Technologies, Inc., for converting one form of bar code to another form of bar code. In this system, a laser beam is modulated using bars and spaces of the scanned symbol. According to the publication, the resulting digitized bar pattern is then decoded by a computer, using an algorithm, to a binary equivalent form from which a bar code representation can be generated that emulates the output of a manually scanned wand. This system, however, is not directed to converting a non-bar code symbology to a bar code symbology such as ASCII, and would appear not to utilize various other features found in the present invention.